Keratin 8 (K8) and keratin 18 (K18) are the first intermediate filament proteins to be expressed during murine development, and represent the evolutionary ancestors of the more specialized keratins. In humans, K8 and K18 are the predominant intermediate filaments of internal organs and carcinomas of breast, liver, and intestine. Recently we have shown that oncogenes which activate the ras signal transduction pathway stimulate K18 expression through regulatory elements recognized by members of the ets and AP1 transcription factor families. In addition, we have generated mice which carry a null allele for the mouse K8 gene and shown that this gene is vital to the development of the embryo. This proposal focuses on both the regulation and function of these intermediate filaments. The functions of these proteins during both normal development and in tumor cells will be investigated with the use of gene targeting technology to generate mice and cells which lack these proteins. In particular, the possible function of these proteins in the invasive motility of both breast and melanoma tumor cells will be tested. The regulation of the K18 gene will be investigated by identifying both the trans-acting transcription factors necessary for expression and the sequences important for directing the gene to a chromatin state, either permissive for expression or incompatible with expression in different adult transgenic mouse tissues. Furthermore, because Kl8 expression in transgenic mice is found to be independent of its site of integration, efficient and directly proportional to the number of integrated genes, we will identify the sequences which are able to confirm these properties on heterologous genes.